Faculty of Biological Sciences, University of Leeds

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Primate Taxonomy

Dr. Bill Sellers

In the last lecture I introduced the general ideas of evolution and
taxonomy. Now it's time to look at how this relates to the evolution of
humans. (# slide of geological time scale) To some extent, factors
shaping human evolution started back at the creation of the universe.
Certainly, the origin of the earth is important, as is the first life
appearing on it. From there, we have the origin of complex single celled
organisms (protozoa), then multi-celled organisms (metazoa), animals
with backbones (vertebrates), first land vertebrates, and even mammals.
Traditionally, however, we limit the study of human evolution to the
study of just our own mammalian order: that of the primates (order primata).

The aim of this lecture is to discuss what a primate is, and to
introduce you to the range of primates present in the world today. I
will show you some pictures, but I don't expect you to remember all the
names, and you certainly won't be asked to identify any of these animals
in an exam, but an appreciation of the wide variation in these animals
is essential for when we come on to discuss how they, and consequently
how we might have evolved.

As I talk about the primates, I will
attempt to map out a likely family tree, concentrating more on the
animals that are most similar to ourselves. This relationship should
become clearer as the course progresses.

Like many definition, the definition of what makes a primate
(as opposed to a rodent, or a carnivore etc.) is complex. There is
little argument as to the core groups of animals today that are primates
as I will be illustrating later, but as one goes back in the fossil
record, there is more dissension. Still, a purely descriptive definition
is needed as a starting point:

Unguiculate, claviculate,
placental mammals, with orbits encircled by bone; three kinds of teeth,
at least at one time of life; brain always with a posterior lobe and
calcarine fissure; the innermost digit of at least one pair of
extremities opposable; hallux with a flat nail or none; a well developed
caecum; penis pendulous; testes scrotal; always two pectoral mammae.
(Mivart 1873)

Unguiculate - possessing nails, hooves or claws

Claviculate - possessing a clavicle (collar bone)

This has been
brought up to date with little change by Le Gros Clark 1959:

At first view, this seems OK
(apart from the dreadful language which makes the whole thing read like
a life insurance document). But there are problems with this definition:

Firstly, there is no unique characteristic that defines a primates. It
is a list of shared characteristics and trends - most of which aren't
even derived, but are retentions of ancestral features, which is
definitely not good.

Secondly, many of these features are
behavioural, or depend on soft tissue anatomy. They won't help us
identify a fossil primate.

Fortunately, there are a number of
very specific features that we can use, such as details of the bones of
the foot and skull, but even so, it can be difficult, especially when
dealing with very early mammals, to decide whether they are primates or
not. There are even certain modern groups, such as the tree shrews (#
slide of tree shrew) that some authors consider to be primates - though
in general, most people classify them separately. In fact bats are
sometimes now considered to be the closest relative of primates!

As
I mentioned before, there are an awful lot of different ideas about the
details of primate classification. I shall largely use this simplified
version (# P.14 NHOTP as OHP and annotate the corrections), but if you
want to see others, then you should look at appendix D at the back of
Conroy's "Primate Evolution". And if you do, don't worry about it too
much!

Do humans fit (# P43 PM)? Discuss...

One of the
things you will have to get used to throughout this course is multiple
names for very similar things. This generally results from a combination
of history, and peoples desire to name things. Primate taxonomy is one
such area:

First primate like animals appeared in the Palaeocene (70
mya), perhaps even late Cretaceous. These are described as early
prosimians.

But what are prosimians? (# P15 NHOTP) Give brief potted
history of all I can remember about these animals...

Remember
that Madagascar was probably colonized by a chance rafting of an early
prosimian in the Eocene (50 mya), which then adapted to fill the
available niches in a similar fashion to the Galapagos finches. (In
fact, it seems likely that Madagascar was colonised by a small number of
events - probably 2).

As you saw from the
diagram, there is a big split between the prosimians on the one hand and
the anthropoids on the other, with tarsiers somewhere in the middle. The
position of the tarsiers is still a major question in primatology.
However, it has been largely resolved by a change of nomenclature.
Prosimians becoming strepsirhini andanthropoidsbecominghaplorhini. By this definition, tarsiers become
haplorhines, and the problem neatly goes away. Taxonomists don't like
trichotomous branches. (Oddly enough, lots of these branches have the
word "rhine" in them. This is from the Greek rhis, rhinos
meaning nose, and generally refers to specific nasal anatomy that can be
used to distinguish these groups. Strepsirhines have dog-like, wet
noses, whereas the rest of the primates have dry noses.)

First
haplorhines (single noses), appeared in the Eocene. This group may be
ancestral to the rest of the anthropoids.

And these infamous
tarsiers? (#P17 NHOTP) Give brief potted history of all I can remember
about these animals...

Here our geography and our classification meet. The
infraorders of platyrrhines (flat noses) and catarrhine (down facing
noses) coincides neatly with the animals found in South America (the
"New World") and with those found in Africa and Asia (the "Old World"),
so the terms are almost synonymous. New World Monkeys are all
platyrrhines, but catarrhines include apes as well as OWMs.

South
America was isolated from the rest of the world in the Eocene and
Oligocene. It seems to have been colonised by early anthropoids, either
from Africa or North America via some sort of land bridge, of floating
vegetation raft about 40 mya (end of Miocene). Thenceforth, these
monkeys have developed independently in quite a distinct pattern. New
World monkeys are every bit as advanced as Old World monkeys with some
very impressive adaptations that the OWMs lack such as prehensile tails.
Interestingly, there are no prosimians in the New World. Their nocturnal
insectivorous niche is taken up by other mammals such as opossums (South
American marsupials), though there is also one nocturnal NWM, Aotus,
the owl monkey (# P115 NHOTP).

And draw up the NWM bit of the
tree.

There are no extant primates in North America even though
it is where some of the oldest primate fossils have been found. There
isn't a good explanation for this.

Or great apes (&
humans). Orang-Utans of Borneo and Sumatra; Gorillas of central Africa;
Chimpanzees - central Africa but more widespread; and Humans - almost
everywhere. Early hominids/pongids appeared in the Miocene (20 mya).